Hobs with inserted edge teeth



April 14, 1959 w. LINDNER j HOB'S' WITH IINSERTED EDGE TEETH File d May 4, 1956 s Sheets-Sheet 1 m eman' WOLFRAM LINDNER ATTORNEYS April 14, 1959 w. LINDNER 2,881,508

Ross WITH INSERTED EDGE TEETH Filed May 4. 1956 v I 5 Sheets-Sheet 2 Jaye/760;:- WOLFRAM LINDNER ATTORNEYS April 14 1959 v w. LlNDNER' 2, 0

' HOBS WITH INSERTED EDGE TEETH I Filed ma 4 195's z Sheets-Sheet a;

jm eman' WOLFRA M LINDNER MM4 7 M ATTOFZ'NEGVYS United States Patent HOBS WITH INSERTED EDGE TEETH Wolfram Lindner, Stefansbecke, near Gevelsherg, Germany, assignor to W. Ferd. Klingelnberg Siihne, Remscheld-Berghausen, Germany This invention relates to hobs for use in .gear cutting andh more particularly to a hob having inserted cutting tee Hobs are known which incorporate a plurality of discs having straight faces on either side and in which each disc carries cutting teeth for approximately one full turn of the hob. This division of the hob into a plurality of separate tooth-carrying discs permits sharpening the hob teeth on conventional machines, with a positive rake angle 7 and corresponding good cutting efficiency. A hob designed to include a plurality of discs as just stated permits the inserted cutter members to be mounted on the discs by transverse wedges which can also take the form :of taper pins. The wedge effect insures that the cutters are located on the hob disc under a pre-load or tension. Damaged or worn cutters can easily be changed and renewed in the existing disc body. with positive rake angle 7 (Fig. 1) on the tooth flanks and '7' on the crest (Fig. 4) is also provided for on the cutters.

A problem which arises in mounting cutting teeth on discs of the type just described in that where the hob teeth lie on the spiral worm thread of the generating worm difiiculty is encountered in mounting the teeth adjacent the edge portion of the disc body since the taper pm which secures the cutting teeth to the disc should be in contact with the disc body on either side of the tooth. For this reason, in prior art hobs formed of two or more discs and having inserted cutting teeth, cutting teeth are usually omitted in the region of the joint between adjacent discs, thereby interrupting the continuity of the cutting teeth.

Accordingly, it is an object of this invention to provide a construction which permits a continuous uninterrupted row of cutting teeth on a hob formed of a plurality of separate disc members, while at the same time retaining the advantage of the alternating cut with positive rake angle and ease of sharpening on conventional machines.

It is another object of this invention to provide a hob construction which includes inserted cutting teeth adjacent the edges of the hob.

It is still a further object of the invention to provide a hob construction having inserted teeth which are held in position on the hob disc with a pre-load or pre-tension.

In achievement of these objects, there is provided in accordance with this invention a hob formed of a plurality of disc members having faces in abutting relation to each other, and in which the bores which receive the inserted edge teeth are offset from the symmetry line of the generating worm adjacent the edges of the disc although the cutting teeth received in these bores lie on the symmetry line of the generating worm. The inserted teeth are held in position by taper pins which are received in slots in the spigots of the cutting teeth in such a manner as to pre-load or pre-tension the cutting teeth.

Further objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

The alternating cut lice Fig. 1 is a top plan view of a two-piece hob with alternating flank cut and positive rake;

Fig. 2 is an elevation view, partially in section, of an inserted hob tooth with a retaining spigot;

Fig. 3 is a development of the circumference of a twopiece hob showing the arrangement of the locating holes for the inserted teeth in accordance with the invention;

Fig. 4 is an elevation view of a modified form of hob tooth inserted into a mounting slot with ears;

Fig. 5 is a view in vertical cross section of the tooth assembly of Fig. 4;

Fig. 6 is an elevation view, partially in section, showing still another form of tooth, with the inside tooth shown in dotted line;

Fig. 7 is a side view of Fig. 6;

Fig. 8 is a top plan view of the center disc of a threepiece hob showing the mounting slot for the inserted teeth;

Fig. 9 is a diagrammatic of the lead of worm SS and also of the direction FF of the mounting slot for the inserted cutting teeth;

Fig. 10 is a diagrammatic view of the lead of worm SS and its relation to double mounting slot RH and 2 2;

Fig. 11 is still another form of view in elevation, and partially in section, of a hob tooth with a cross piece for locating;

Fig. 12 is a side view of Fig. 11;

' Fig. 13 is a View partially in elevation and partially in vertical section of a three-piece hob with conical basic form;

Fig. 14 is a diagrammatic top plan view illustrating the position of the discs during sharpening;

Fig. 15 is an elevation view of a hob tooth whose retaining spigot is secured by a taper pin which engages the outside surface of the spigot;

Fig. 16 is a view in horizontal section of the hob tooth of Fig. 15;

Fig. 17 is a view in vertical elevation, partially in section, of a hob tooth secured by a cross piece and an outside taper pin; and

Fig. 18 is a diagram showing during the alternating cut.

Referring now to the drawings, and more particularly to Figs. 1-3, inclusive, the hob comprises a pair of disc members 20 and 22, each disc having one face in abutting relation to one face of the other disc. Cutting teeth Z through Z lie on disc 20, while cutting teeth Z through Z lie on disc 22, these teeth lying on a spiral which conforms to the generating worm. It will be noted from an examination of Fig. 1 that the teeth extend continuously even in the region of the joint between discs 20 and 22. Although the cutting teeth themselves all lie on the generating worm, the locating bores 24 which receive the spigots 26 of the cutting teeth do not all lie on the generating worm. Thus, as seen in Fig. 3, the bores 24 for teeth Z through 2,; of disc 20 and the bores for teeth Z through Z of the disc 22 all lie in the direction of the lead of the generating worm. Teeth Z through Z and Z through Z are hereafter described as inside teeth and are all uniform except for a possible variation in the height of the teeth due to the lead-in. However, the bores which receive the spigots of teeth Z through Z of disc 20 and of teeth Z and Z of disc 22 do not lie on the lead of the generating worm but are offset from the face of their respective disc nearest the adjoining disc by a distance D as indicated in Fig. 3 and also in the modified tooth of Fig. 5. Thus while with the inside teet the center lines of the retaining spigots and the symmetry line of the generating worm substantially coincide, the center line of the retaining spigots for the edge tee is offset relative to the symmetry line the varying tooth length of the generating worm to the extent of the variable distance y (see Fig. 5) so that the edge hob teeth follow the worm thread although the bores of the retaining spigots for the edge hob teeth do not.

' The inside teeth are interchangeable, except for a variation in lead-in height. The edge teeth, on the other hand, differ from one another since the dimension y increases from one tooth to the next. With the hob construction of the invention, the joint TT in Fig. 1 between the individual hob discs 20 and 22 has no effect on the cutting teeth. The cutting teeth project fully or partly beyond the disc in which their respective spigots are mounted and into the adjacent hob disc, and can exert their cutting effect over their full length. The adjoining disc to that on which the edge tooth is mounted is preferably indented adjacent such an edge tooth in order to avoid sharp corners and recesses and to insure smooth contours of the delicate cutters. In the modified form of Fig. 6, the disc 28 is indented as at 30 in order to allow the edge tooth 32 of disc 34 to be constructed with an inclined back 36. In addition, in Fig. 6 the bore 38 of the retaining spigot 40 for edge tooth 32 is inclined rela tive to the hob axis. The form of tooth 32 is thus also well suited for absorbing the forces applied to teeth located at positions corresponding to the positions of teeth Z and Z in Fig. 3 which project farthest beyond the respective discs.

Edge teeth are therefore always located at the joint between two hob discs. In the case of two-piece hobs such as those of Figs. 1-7, they are situated on the side next to the adjacent disc, as no limitation in respect of width exists on the other side; i.e., towards the outside. In the case of three-piece hobs, the edge teeth on the outer disc must only be on the inside edges of the respective discs. On the center disc of a three-piece hob,

the edge teeth are on both sides of the center disc.

There is shown in Fig. 8 the arrangement of a slot 42 for receiving the base portions or spigots of cutting teeth on the center disc 44 of a three-piece hob. This slot 42 contains a slot section BC for the inside teeth which lies along the lead of the generating worm. At the opposite ends of slot portion BC are provided slot portions AB and CE which lie parallel with the face of the disc. Slot sections AB and CE are provided for the edge teeth of the center disc 44 shown in Fig. 8.

Instead of having the bores of the edge teeth mounte in a slot which is parallel to the face of the disc, the mounting slot or the row of bores for receiving spigots of both inside and edge teeth may be given a lead in the direction FF (Fig. 9) which is smaller than the lead SS of the generating worm. The lead angle a of the mounting slot or row of bores is therefore smaller than the lead angle of the generating worm. The respective angles are subtended between the mounting slot or row of bores and a line parallel to the disc face 46 in the case of lead angle 6;, and between the generating worm and the parallel line in the case of a If in an extreme case 5;:0, the end of the resultant annular slot will coincide with the start of the slot and the entire surface of the base flange of the tooth can then be located in the slot instead of the narrow surface p (Fig. 5) which is used on the outside and inside diameter of the slot on account of the varying lead angles.

In the mounting arrangement shown in Fig. 9, only the mounting of the hob tooth at the center M lying at the intersection of line FF with line SS is symmetrical with respect to the lead of the generating worm. The mounting slot or bores for all of the other teeth are offset from the lead of the generating worm up to the maximum distance y (Fig. 5). If distance y is to be reduced in order to reduce fiexion, it is possible to use in place of one mounting slot FF running around the full circumference two slots HE and F F (Fig. 10) running around half the circumference, ofiset from a line parallel to the face of the disc 48 by about half the lead of the worm. Points M and M each carry a symmetrical tooth as the direction of the lead SS of the generating worm coincides with the center of the mounting slots and the center of the row of bores F F or F F as the case may be. The maximum offset y is thus reduced by half.

As seen in Figs. 11 and 12, the cutters 50 can also be located in longitudinal dovetail 52 running across the full width of the hob disc 54 or 56. The member 58 of the cutter can then be spread by the taper pin 60 and pressed onto the disc 54 with a downward pre-load or pre-tension.

In the construction of Fig. 11, the hob teeth of inside cutters lie axially towards the outside as indicated by the dotted flanks above the longitudinal member 58. With edge teeth, part of the profile, or the entire rolling profile lies outside the face of the hob disc. The adjacent disc is recessed as at 62 on disc 56 to receive the projecting edge teeth.

The present construction in which the edge and inside teeth are mounted in diiferent ways makes possible the use of inside teeth which are integral with the discs, with the outside or edge teeth being formed by specially inserted cutters. This is particularly economical in the case of small profiles.

In the case of taper hobs as shown in Fig. 13, used for producing spiral bevel gears, solid teeth 64a, 66a integral with the discs may be used on the discs of the smallest and intermediate diameters; namely, the discs 64 and 66 in Fig. 13. The discs 64 is manufactured in one piece integral with the shank portion of the hob. The disc 68 is integral with the retaining taper and is provided with inserted edge teeth 70 at the joint between discs 66 and 68.

One advantage of dividing the hob into individual discs is that it permits diflferent relative positions of the discs during gear cutting and sharpening. For sharpening, the discs are so turned in relation to one another that one part, i.e., for example the left-hand cutting teeth, are traversed by the grinding wheel. The discs are subsequently turned to the required position for the other half of the teeth with the other direction of the lead and are then reground. The working position of the hob teeth can be selected so that the teeth of the adjoining disc are in the recess of the first disc, Fig. 1, provided that the flank cutting faces are on the generating worm.

If it is adequate to sharpen the discs separately, the individual discs can carry different numbers of teeth on their periphery. This can be of advantage if the finishcutting part of the hob is in the proximity of the rolling point of a greater number of cutting faces in order to envelop the tooth profile more accurately. In other words, the disc which is in the finish-cutting part of the hob includes a greater number of teeth on its periphery than does the adjacent discs which lie in the rough cutting portion of the hob. It is particularly advantageous to use taper hobs, as shown in Fig. 13, with increasing numbers of teeth with an increasing diameter of the discs. This type of hob can, of course, also be made with multistarts. The rows for the mounting holes and the mounting slots shown in Figs. 3, 8, 9 and 10 are repeated twice in the case of a two-start or double-threaded hob and three times over the full circumference in the case of a three-start hob.

Figs. 15 and 16 show an arrangement in which the cutting teeth 72 are mounted using taper pins 74 which engage the sides of the spigot 76 of the cutters rather than passing through a slot in the spigot. The view shown in Fig. 15 of a cutter 72 with retaining spigot 76 shows that arranging the taper pin 74 on the side grips more material towards the edge.

Fig. 17 shows a taper pin 78 employed to pin a tooth 80 to a disc 82 in the case where a dovetail 84 receives the spigot 86.

If the teeth are divided into alternately right and left cutting ones, the length of the teeth vary unless an axial displacement of the disc during indexing is contemplated. This arrangement is shown in Fig. 18. The slots run from the perpendicular to the lead of the worm having a lead angle alternately and -'y. With a uniform index angle this necessitates a variation in the length of the hob teeth. Fig. 18 shows that the odd numbers of teeth from 1 to 9 increase in length, while the even numbers of teeth from 2 to decrease. The error becomes smallest if, as shown, the center teeth 5 and 6 are of the same length. During manufacture it is therefore essential to index the right-hand flutes first. If the number of teeth is Zn, an index plate with Zn/ 2 flutes is used to obtain the flutes 2, 4, 6, 8 and 10. For changing to the left-hand flutes, the flute center P is determined as the line halving P and P and the index plate previously used is indexed in the normal way. The center teeth are provided with a scale to enable grinding the same amount off both flute leads. In case of hobs with tapered base body as shown in Fig. 13, with the same number of teeth on the three hob discs, the scale divisions are proportional to the center diameter of the individual parts. If the numbers of teeth on the three discs differ, the scale divisions must be of dimensions corresponding to the various lengths of the center teeth on each disc. The design described can be applied to hobs for producing all profiles lending themselves to this machining method, such as spline shafts and other workpieces.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and, therefore, it is aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as my invention is:

1. A gear cutting hob comprising *a cylindrical body member consisting of a plurality of axially aligned circular segments positioned in abutting relation, a plurality of cutting teeth extending circumferentially about each segment along a helical line with respect to the body axis, at least one of said teeth overlying the joint between adjacent segments and others of said teeth being spaced axially from said joint, and means connecting each cutting tooth to the segment with which said tooth is associated, the connecting means for the tooth overlying said joint being ofiset from said joint and from said helical line, and the connecting means for the teeth spaced axially from said joint being located along said helical line.

2. A gear cutting hob according to claim 1 wherein the connecting means for the tooth overlying the joint between adjacent segments is detachable from the segment with which said tooth is associated and the connecting means for the teeth spaced axially from said joint are integral with the segment with which said teeth are associated.

3. A gear cutting hob according to claim 1 wherein all of said connecting means are detachable from the segment with which said cutting teeth are associated.

4. A gear cutting hob according to claim 1 wherein the cutting teeth associated with one of said segments extend along a plurality of helical lines with respect to the body axis.

5. A gear cutting hob comprising a cylindrical disc, a plurality of cutting teeth extending about the circumference of said disc along a helical line with respect to the disc axis, at least one of said teeth overlying an edge of said disc and others of said teeth being spaced axially from said edge, and means connecting each tooth to said disc, the connecting means for said overlying tooth being spaced axially from said disc edge and being olfset from said helical line, and the connecting means for the teeth spaced from said disc edge being located along said helical line.

References Cited in the file of this patent UNITED STATES PATENTS 530,793 Odgers Dec. 11, 1894 1,049,589 Mitchell Jan. 7, 1913 1,194,865 Muller Aug. 15, 1916 1,278,629 Francis Sept. 10, 1918 1,495,067 Conklin May 20, 1924 1,615,969 West Feb. 1, 1927 2,310,826 Adams Feb. 9, 1943 FOREIGN PATENTS 901,653 France Nov. 13, 1944 903,772 Germany Oct. 25, 1954 911,933 Germany May 20, 1954 

